Electrochromic (EC) devices have many applications, some of them are automotive mirrors, car glazing including sunroofs, glazing for other transportation means such as boats, planes, trains, buses, etc., and for architectural glazing applications for interior and exterior uses. Briefly, EC devices are made by sandwiching an electrolyte between two coated substrates. Many examples of such devices are shown in U.S. Pat. No. 6,317,248 which is incorporated herein by reference. To operate these devices, electrical power is applied across the electrolyte cross-section via the coatings on the substrate, so that a movement of the charged species (ions or polarized particles) takes place. These ions are transported via the electrolyte to the electrode surfaces for further reactions to take place which gives rise to color change or change in optical density. This change is varied reversibly at the discretion of the user.
As used herein, the terms electrochromic device are intended to also include devices in which polarized particles are not transported across the electrolyte for a color change, but instead simply re-orient themselves as in liquid crystal devices and suspended particle devices. In addition, other user-controlled variable transmission devices employing similar principles of construction, i.e., an active material sandwiched between the two substrates, such as “user controlled photochromic devices are also intended to be embraced by these terms. Such laminates may also be incorporated in window systems where additional glass elements are used (e.g., insulated glass units) where these additional elements may not be laminated.
While it is conventional practice in electrochromic devices to use a liquid electrolyte or a solid electrolyte, as shown, for example in U.S. Pat. Nos. 6,154,306 and 5,856,211, such prior approaches have not resulted in an electrochromic device that exhibits characteristics common to conventional (non-electrochromic) laminated glasses such as those made by laminating polymeric sheets Safelex™ (Solutia, Saint Louis, Mo.) or Butacite™ (Dupont, Wilmington, Del.). Safety, in the context of applicable building industry and automotive industry standards, is defined not simply as preventing leakage of the electrolyte from a broken laminate, but containment of the pieces of broken glass to avoid injury to the occupants in case of impact.
One might suppose that it would be straight-forward to produce an electrochromic device that could exhibit the attributes of safety glazing by interposing between the substrates a polymeric sheet for glass lamination such as those made of polyurethane, PVC or polyvinylbutyral, including Butacite™ from Dupont and Safelex™ from Solutia Springfield, Mass. However, an electrochromic device requires chemically active contact between the electrolyte and the coated surfaces of the substrates which would be prevented by such ordinary plastic sheets without modification. Modification, such as addition of plasticizers by soaking could compromise their ability to impart safety attributes. Accordingly, it would be advantageous to achieve an electrochromic device that would exhibit the characteristics of impact-resistant safety glass. Moreover, a mandated use of tempered glass would not be satisfactory as it limits the type of transparent conductors and other coatings that can be used with electrochromic devices. Assembled EC devices made of glass substrates may be laminated with external sheets of polymeric material, such as Spallshield™ (Dupont, Wilmington, Del.) to yield impact resistant laminates. However, these post processes cost and the scratch resistance of the polymeric sheets is usually not as good as glass.